Raw diets are touted as the best diet for ferrets, as they are obligate carnivores (derive all necessary nutrition for meat). Feeding raw is very big in the UK, as the availability of quality kibble is lacking, though the quality of a lot of ferret kibbles in the US is lacking as well. Fortunately, there are some good cat kibbles available.

I don't have the time right now to switch my ferrets to raw (they can be notoriously picky) but they do occasionally get a "soupie" made from commercial frozen Natures Variety Instinct raw. Their main diet consists of 3 high quality meat based kibbles.

I've been really happy with the quality of Natures Variety (both kibble and raw). They make raw diets for dogs.
Another brand I know of is Stella and Cheweys.